In recent years, since a large display device such as a liquid crystal television is increased, a display device such as a liquid crystal display device or a light-emitting device has been actively developed. In particular, a technique where a pixel circuit and a driver circuit including a shift register circuit or the like (hereinafter described as an internal circuit) are formed over the same substrate by using transistors which are formed by using an amorphous semiconductor over an insulator has been actively developed, since the technique greatly contributes to low power consumption and low cost. The internal circuit formed over the insulator is connected to a controller IC or the like arranged outside the insulator (hereinafter described as an external circuit) through a FPC or the like, and its operation is controlled.
In addition, a shift register circuit which is formed by using transistors made of an amorphous semiconductor has been devised as the internal circuit formed over the insulator (see Reference 1: PCT International Publication No. 95/31804).
However, since the shift register circuit has a period in which an output terminal is in a floating state, noise is easily generated in the output terminal. Due to the noise generated in the output terminal, a malfunction of the shift register circuit occurs.
In order to solve the aforementioned problems, a shift register circuit where an output terminal does not become a floating state has been devised. This shift register circuit is operated by a so-called static driving (see Reference 2: Japanese Published Patent Application No. 2004-78172).
The shift register circuit disclosed in Reference 2 can realize the static driving. Therefore, the output terminal does not become a floating state in this shift register circuit so that noise generated in the output terminal can be reduced.